DESCRIPTION (from the investigator's abstract): Soon after birth, most infants develop near emmetropic refractive errors which are then maintained in both eye throughout childhood and into early adult life. However, for reasons not currently understood, a significant and increasing proportion of the population develop abnormal refractive errors (currently about 30 percent of young adults have significant refractive errors). In addition to the high costs for traditional optical corrections, refractive errors can lead to permanent sensory disorders and ocular abnormalities causing blindness. The long-term objectives for the proposed research are to provide a better understanding of the etiologies of human refractive errors and to gain insight into refractive errors as risk factors for the development of sensory disorders like amblyopia and anomalous binocular vision. A primary goal is to determine how early visual experiences, and in particular optical defocus, influences ocular refractive error development. Spectacle lens-rearing regimens will be used to effectively alter the refractive status of infant rhesus monkeys. Optical and ultrasonographic techniques will be used to quantify the effects of these lens-rearing strategies on the development of the eye s axial and refractive components. In addition to determining which ocular components can be influenced by visual experience, the proposed investigation are designed to determine (1) whether the emmetropization process in higher primates is sensitive to and regulated by optical defocus, (2) the relationship between the phenomenon of form-deprivation myopia and the normal emmetropization process, and (3) whether the presence of astigmatism disrupts normal emmetropization. Parallel psychophysical investigations of spatial contrast sensitivity and stereoacuity will examine the relationship between early refractive errors and the development of amblyopia and/or anomalous binocular vision. The behavioral studies will also determine whether the presence of sensory disorders, themselves, can disrupt emmetropization and promote the subsequent development of abnormal refractive errors. The results of these studies are essential for the development of new treatment and management strategies for refractive errors. Moreover, these investigation will help determine the extent to which refractive errors need to be corrected in young infants in order to avoid the development of sensory disorders.